Weather Forecast

New fruit fly threatens Minnesota berries

The tiny spotted wing Drosophila is native to Asia. It was first found in the U.S. in 2008, in California, and quickly caused sizeable losses along the West Coast. The pest's first arrival in Minnesota was detected late last summer, and the state's raspberries, strawberries, blueberries, blackberries, grapes, cherries and plums are all vulnerable, the St. Paul Pioneer Press reported Wednesday.

The first confirmed appearance in Minnesota this year was on June 27 on grape vines in Dakota County. The discovery dashed hopes that the flies would not survive the severe winter. An infestation was found in summer raspberries in Rice County a week later. At least five more reports have since surfaced since then, and officials say the pest could be present in other Twin Cities metro-area counties as well. It turned up in 29 Minnesota counties last year.

"It's somewhat of a silent infestation," said entomologist Mark Asplen of the University of Minnesota. "The flies lay their eggs inside the fruit, the eggs hatch and the larvae start feeding on the fruit from the inside. The fruit becomes this kind of mushy mass. There's no human health issue with this. It's more of a quality of the fruit issue."

Asplen said the maggots hit fall raspberries hard last year. Some pick-your-own growers had a 50 percent loss and had to shut down, he said.

Officials urge berry and grape growers to check for the pests and take action, but they concede the fly is so new to Minnesota that there's a lot they still don't know.

The key, Asplen stressed, is detecting the problem early.

"It is manageable with insecticides," he said. "If you can detect it and treat it early enough, you can salvage your yield."

While that may be a solution, it's not a welcome prospect for a business built on pick-your-own farms, summertime family outings and plucking ripe berries and popping them into your mouth.

"Historically, most berry growers in Minnesota have not had to use any insecticides, particularly during the late-season harvests," said Bill Hutchinson, another University of Minnesota entomologist. "This pest could be a true game changer for the Minnesota berry industry."

The spotted wing Drosophila is a small fly, only 2 to 3 mm long, yellowish brown, with prominent red eyes.

State and university officials recommend a three-pronged strategy to fight back. Berry growers should set up monitoring traps; dispose of overripe fruit, which is most attractive to the pests; and contact the Minnesota Department of Agriculture for details on how to control the pests with insecticides.